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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Rich or lean
Post Info TOPIC: Rich or lean
Aidan


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Rich or lean
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i have found some syptoms i will underline and bold my syptoms

Rich Symptoms:

  • Poor power output
  • Starts too easily when cold - requiring little or no choke. Responds readily to the throttle when cold. Runs worse as it warms up
  • Hard starting when hot
  • Ragged idle...due to "loading up" of unburnt fuel
  • Idle that tends toward lower rpms than expected based on the setting of the curb idle screw
  • Easily settles to idle, but has tendency to dip below set idle speed then recover...sometimes stalls
  • Strong pungent odor of unburned fuel
  • Buildup of black, dry, sooty carbon deposits on spark plugs. Bad cases of this buildup will foul the plug completely and kill that cylinder.
  • Excessive buildup of dry sooty deposits in the exhaust system
  • Responds to throttle, but sluggish
  • When fully warmed up, runs much worse when choke is applied.
  • Poor fuel mileage
  • Black "puffy" smoke during hard acceleration
  • Temporarily removing air filter element makes the engine run better.
  • Runs worse as you climb to higher elevations
  • Fresh engine oil quickly turns black from excess fuel dilution

Lean Symptoms:

  • Poor power output
  • Hard to start when cold - requires excessive choking.
  • Lengthy warm-up required.
  • Runs better (but not good as it warms up)
  • Spark plugs overly clean..with no deposits or slight glazed appearance
  • Rough, erratic idle that drifts toward higher rpms than expected based on the setting of the curb idle screw. Sometimes a lean condition will cause a "hanging" idle that is slow to settle down to set idle speed.
  • Backfiring
  • Sluggish...hesitates when the throttle is opened, then recovers (often accompanied by a slight backfire) (only when to higher gear is selected, but i asume that jsut coz the reves are not high enough)
  • Vague throttle response
  • Surging at steady throttle cruise operation
  • When fully warmed up, runs better when choke is applied.
  • Engine runs hotter than normal. Headers can turn cherry red in extreme cases!
  • Temporarily removing air filter element makes the engine run worse.
  • Unusual "sucking" noises in the intake area.
  • Runs better as you climb to higher elevations
  • Slight back-firing on deceleration. This normal tendency is controlled by the air cut-off valve(s) operation. If the air cutoff valve(s) is working properly and you still have backfiring on deceleration, something is causing a lean condition.

 

so im confused lol

anyone else got the same

http://www.randakks.com/TechTip72.htm



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Aidan


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my spark plug, held the revs on the engine steady, then turned off.

its a light black carbon deposit. not as dark as iv seen and deffiantly not "white" like the lean option." so im confused

spark plug.JPG



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TTRfan


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Wow - that is an excellent diagnostic list Aidan! Can I make it a sticky?

Backfiring can also be caused by an air leak in the exhaust system.

There could also be an intermittent mixture problem if the inlet stub between head and carb is coming apart.

Brian



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Aidan


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Well I thought my bike was running rich as the spark plug has a sooty black appearance. ( not shinny black) However I read that if ur exhaust makes a popping sound it's lean.. My exhaust makes this on deseleration. ( i always thought this was maybe a bit of extra fuel burning). Any ideas?? The exhaust is an aftermarket one

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Aidan


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Yeah go for it. Now my questions.

1. Air leak.. As in possible where the header joins on?
2.inlet stub twist head? What is this? And how do I fix it?

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TTRfan


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I guess there are two possible areas for leaks:

1. Between the head and header pipe - unlikely and I think you would hear this - could easily be sealed with a bit of high temperature silicone sealant just in case...

2. Between header and silencer - much more likely. The cure depends on the type of joint. If the new silencer uses one of these then they work very well and it might be just a case of tightening the clamp a little more. If it is a metal to metal join then use some exhaust paste. Don't put it on the silencer but on the end of the header pipe - that way it doesn't fall into the silencer upon assembly.

Sorry for use of antiquated language - "twixt" means between so I have edited it - see here  for what I mean.

Another less likely cause of popping is a leaky exhaust valve allowing unburnt mixture into the header. Did the popping only start with fitting the new silencer? If so, that isn't likely to be a cause.

Brian



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Aidan


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Well I'm almost 99.9% sure that there might be some air getting in between the muffler and the head pipe, I seem to recall some fumes coming out there after the exhaust system had been cleaned. ( the joint) so il dump some high temp gasket sealent on there tomorrow.

The popping sound is not that bad really it's just that I wanted to make sure it wasn't anythig to bad ( eg running to lean and damidging my bike)

Thanks!

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Aidan


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no worries mate

IMGP6760.JPG

IMGP6759.JPG



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Aidan


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All fixed just pumped some high temp instant gasket on the header and put it all back together. Engine is now running smoother as well. Its amazing that one little leak makes so much differance

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davecambo


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Aidan i sent you a PM

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davecambo


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hey can you post a large picture of your avatar please? that looks cool.

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davecambo


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Have you checked your plug again, it may still be running rich mate. Mine is even after snorkel and staintune exhaust

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Aidan


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Yeah I have and I'm still very confused it still makes a very slight poping on heavy deceleration ( eg using the engine to help break). I'm wondering if this isn't just because the throttle is closed and this is caused g the engine to lean out while the back wheel is causing the engine to still tick over at a higher speed then the carb wants to let it.

As the exhaust and plug have sooty carbon deposits. My question is.

Do I raise or lower the pin in the carb? To make it leaner? And /or is there something else I need to change. In the carb?

Also is there an upgrade that I can do to get a bit more power out of the carb?


Anouther factor that makes me thing it's running Rich is my oil get dirty pretty fast.


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TTRfan


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What main jet are you running?

If your engine is really running rich then moving the needle a notch or two isn't likely to sort it out.

I can't think why an engine would run OK and then start to run rich. Maybe try it without the air filter and with the airbox cover off for just a short non-dusty run and see what effect that has?



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rattlyolddt


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Check your float height, condition of your carb pump diaphragm and spring, and is the carb clean?

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Aidan


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Carb is cleaned, float pump is working from what I can tell. I moved the needle 1 leaner and it sounds like its alot more responsive . Can't really take it round the block for a spin as we have some idiot on a 2 stroke down the road that rips burnouts ect so the neighbors are very moody about trail bikes.

Will test it out ASAP see if it's fixed

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Aidan


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Forgot to mention the main jet is 95b0 and the needle is 5c9c what ever that means

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Aidan


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Ok so I installed some new indicators on the bike and decided to start her up with kick start ( first attempt ever) very glad it works. How ever after a few minutes the bike now seems to be running lean. Backfiring and stalling when the throttle is open. Soooo confused

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TTRfan


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That seems to indicate a jet blocked. Could you have somehow got water into your tank and carb?

If you get a droplet ofwater under the main jet it can sit there whilst on low revs (water heavier than petrol) but when you open the throttle the extra vacuum lifts the water up to under the jet and effectively blocks it as the water won't go through.

Just a thought.

Brian



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Aidan


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Well it's possible I guess. It was to be coz I'm completely out of ideas lol. My jet ist blocked though as I cleaned it when I took the carb out. Hmmm

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TTRfan


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I have put a few hundred miles on the project TTR's new engine now so have started to give it a bit more throttle. This showed up a carburation problem in that it blubbers when you crack open the throttle until the engine catches up.

I tried pulling out the choke whilst it was doing this and it made it worse so the mixture isn't too lean.

I tried it with the airbox cover off and it pulls a lot better.

So my conclusion is that the carb is over jetted and the mixture too rich.

Simple tests to do.

Just need to whip the carb off now and re-jet it.

Brian



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Aidan


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Ok Brian so tried ur advice. I drained the carb. Then started the bike( which wS hard for some reason). Then after warming up remouved the air box cover and filter this caused it to run rougher. Replaced and then pulled the choke out which stalled the bike. So I think the carb is in the right area now. But it still back fires when the throttle is let go after a heavy rev. I think this is due to the engine still running at a higher rev while the throttle is shut. Causing a lean environment? Or is this due to something else. The bike revs up well and has stoped surging as well as revving down ok. It's just the backfiring. Should I just leave it as is now?

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Cubber


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Backfiring on engine over-run is generally an indication of exhast system leakage.

Check the header connection gasket and muffler joints - then look for pin-holes anywhere in the system that may enable entry of air INTO the exhaust system.

Martyn



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